1. Field of Invention
This invention relates generally to cut resistant yarns and more particularly to cut resistant yarn for gloves or sleeves.
2. Description of Related Art
Knitted “work” gloves formed of conventional materials, such as cotton or poly-cotton provide some measure of protection from injury and some cushioning for the hand of workers, but are notoriously deficient insofar as providing resistance to cutting. Thus, it is a common practice to knit work gloves of cut resistant yarns. Most cut resistant yarns are formed of filaments—i.e., they are a bundle of continuous filaments or fibers. The term filaments and fibers are used interchangeably herein, and may be given the same general meaning, e.g., microscopically, looking like a bundle of fishing lines.
Cut resistance is obtained by several factors. One factor can be deemed to be the tendency to produce “slippage.” In particular, when a blade or other sharp instrument passes over the yarn, it slides along the smooth surfaces of the fiber bundle, rather than catching on the yarn, which action would result in a tendency to cut the yarn. Tensile strength is another factor in establishing cut resistance. In this regard, the shear strength of the fiber is selected to be so strong that it prevents the fiber from breaking. The abrasive action of the fiber is also a factor, since the harder the fiber, the greater the tendency to dull the cutting edge, thereby reducing the tendency of the fiber to be cut. Another significant factor is what may be called “rolling.” This is the ability of the fibers of the yarn to twist or roll about their longitudinal axis as the blade moves across the yarn. Such rolling action enhances cut resistance by denying the cutting edge a stationary surface to cut.
Filament yarns, due to their structure, will not stretch. Stretchability is of considerable importance in order to readily knit a viable, low-cost glove. Consequently, the knitted glove industry, typically plies these yarns with an elastic or stretchable yarn such as Spandex® or Lycra® alongside the filament yarn and then wraps the stretchable yarn under tension in a helical pattern around the filament yarn, with the helix spacing of several twists of stretchable yarn per inch of the filament yarn (i.e., the fiber bundle). When the tension is relaxed, the resulting combined yarn is a stretchable filament yarn that can be knit into gloves or sleeves.
Unfortunately, the plying process forces the filament yarn to twist in the same direction as the stretchable yarn is plied (wound). When this happens two things occur. First, the ability of each fiber of the bundle to roll individually is restricted, thus reducing cut resistance of the combined yarn. Second, the combined yarn then develops a twist to it.
When gloves and arm sleeves are knitted, any yarn that is twisted, such as the combined yarn just described, will cause a torque. When this happens, glove fingers become twisted and arm sleeves begin to wrap around the arm, which can reduce cut resistance because it is now restricting the ability of the sleeve to stretch. The industry calls this torque in the yarn an “S.” To counteract S torque, it is a common practice in the industry to add another yarn twisted in the opposite direction as the stretchable yarn. This additional yarn is frequently referred to as the “Z” or “zed” yarn. The use of a Z yarn in the combined yarn allows the fingers of a glove knitted from the combined yarn to be flat and a sleeve knitted of it to relax. The Z yarn can be of lesser denier than the stretchable yarn and can be wrapped around the stretchable yarn in the opposite direction to counteract the twist. Alternatively, the Z yarn can be of the same denier as the stretchable yarn and can be run parallel to it and the two combined yarns knitted together so that the twist provided by both yarns counteract each other.
While the use of a Z yarn has the foregoing advantage, it is not without cost. In this regard the use of the additional reverse twisted Z yarn increases the cost of the resulting yarn due to the cost of the Z yarn itself. Moreover, if the Z yarn is counter-wrapped about the stretchable yarn, there is the additional manufacturing costs inherent in effecting that wrapping action. If the Z yarn is run parallel to the stretchable yarn and then the two are knitted together, the resulting glove or sleeve will be considerably thicker (which may be undesirable from the standpoint of flexibility). To keep costs down, it is a common practice to use low cost materials for the Z yarn. Unfortunately, such low cost materials are inferior in that they are not cut resistant. When these low cost Z yarns are added to a glove or sleeve, they tend to break down or cut more easily. When this happens the knitted product falls apart.
Thus, while the above yarns may be generally suitable for their intended purposes, they leave something to be desired from one or more of the following factors, ease of manufacture, effectiveness, reliability and cost.